My experiments investigate the effects of brain implants of either testosterone, estradiol, or 5a-dihydrotestosterone into the medial nucleus of the amygdala, the bed nucleus of the stria terminalis, and the medial preoptic area in adult male Syrian hamsters. I am assessing the effects of these implants on the male's attraction to the female hamster's vaginal secretion (FHVS) in tests where no copulation is permitted and the male cannot make oro-nasal contact with these odor stimuli. To evaluate copulatory behavior I am measuring temporal and frequency parameters of mounts, intromissions, and ejaculations, as well as the male's investigation of different regions of the receptive female's body, including specifically the ano-genital region. Androgens are known to affect both the male's responsiveness to FHVS and copulation with females. These behaviors in the male hamster are absolutely dependent upon specific chemosensory stimuli, and many androgen-concentrating neurons are in locations which would permit them to influence, or be influenced by, the neural pathways utilized by these essential sensory cues. I believe these facts make the male hamster an ideal species for studying many aspects of the hormonal regulation of masculine reproductive behavior.